Recovery method of tin and nickel from scraps of steel ball for barrel plating

ABSTRACT

The present invention relates to a method of recovering tin and nickel compounds with high purity at a high yield from scrap steel balls for barrel plating through simple processes without using an excess amount of a solvent, the method using an eco-friendly dry pretreatment and subsequent processes including hydrogen reduction and electrolytic refining under certain conditions.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to and the benefit of Korean patent application No. 10-2012-0037305 filed in the Korea Intellectual Property Office on Apr. 10, 2012, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

In a typical process for preparing electronic parts such as chip parts, e.g., a varistor, a chip inductor, and a multilayer ceramic capacitor (MLCC), an external electrode may not be directly subjected to a soldering process after its termination process is completed, and thus the outermost electrode is sequentially plated with tin (Sn) and nickel (Ni) so as to facilitate the soldering process. Barrel plating has been widely used for this purpose.

In barrel plating, many small sized chips are plated at a time using a rotating type of barrel plating apparatus. The barrel plating apparatus includes a barrel plating bath filled with an electrolyte, a barrel container filled with chip parts to be plated and electric mediums, a rectifier supplying an electric current to the barrel container, and a driving motor for rotating the barrel container.

The chip parts and the electric mediums are mixed in the barrel container. Typically, steel balls with a high level of electro-conductivity are used for such an electric medium, having a diameter in the order of 0.3 to 2 mm. After being used in barrel plating for a certain period of time, the steel balls have a certain thickness of tin and nickel plated on their surface, losing their utility and ending up in waste scrap.

In the past, a wet process utilizing an acidic solution was adopted for the purpose of recovering tin or nickel from the dummy balls of such waste scrap. However, in such methods, the presence of a substantial amount of iron has posed considerable difficulties in recovering tin with high purity. Moreover, since such methods entailed using an excess amount of solvents and chemicals, a large amount of waste was generated, causing problems of environmental pollution and increased costs for treating the waste.

Meanwhile, little research has been made on a method of recovering tin from the dummy balls obtained as byproducts in the barrel plating process for the electronic parts, and a method of enhancing the purity of recovered tin has yet to be known in the art as well.

SUMMARY OF THE INVENTION

The present invention provides a method of recovering tin and nickel compounds, which includes the steps of: subjecting scrap steel balls for barrel plating to a heat treatment at a temperature of 300° C. to 700° C.; grinding and sorting the heat-treated scrap; adding a tin compound and a nickel compound being separated from the grinding and sorting step to an acidic solution; filtering the acidic solution having the tin and the nickel compounds added thereto; subjecting residues from the filtering step to a hydrogen reduction treatment at a temperature of 600° C. to 1000° C. to recover tin; and subjecting the recovered tin to electrolytic refining.

The scrap steel balls for barrel plating include 10 to 98 wt % of an iron component, 1 to 80 wt % of a tin component, and 1 to 80 wt % of a nickel component.

The scrap steel balls for barrel plating may have a spherical or circular shape having a longest diameter of 0.1 to 5 mm.

The scrap steel balls for barrel plating may be dummy balls obtained from the barrel plating process for electronic parts.

After the heat-treatment, grinding the scrap steel balls for barrel plating may be accomplished by using a ball mill or a vibration mill.

The acidic solution to which the tin and the nickel compounds separated from the grinding and sorting step is added may have a concentration of 0.1 to 10 M.

The acidic solution may include nitric acid, or a mixture of nitric acid and hydrochloric acid.

The recovery of the nickel compound may further include a step of adjusting the pH of the filtrate of the acidic solution having the nickel compound added thereto to between 2 and 5 to eliminate an iron component therefrom.

The recovery of the tin and nickel compounds may further include a step of evaporating and concentrating the filtrate from which the iron component has already been eliminated to recover the nickel compound.

The electrolytic refining may be conducted at a temperature of 10° C. to 60° C. with a current density of 0.1 A/dm² to 1.0 A/dm² and a distance between the electrodes of 10 mm to 200 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an actual appearance of the dummy balls together with their schematic structure.

FIG. 2 shows a SEM image of the dummy balls used in the examples.

FIG. 3 shows the results of XRD analysis, which was made on the powders of the tin and nickel components as obtained in Example 1.

FIG. 4 shows data on the metal contents being leached depending on the acid concentration and the leaching time in Example 1.

FIG. 5 illustrates a relation between the standard free energy and the temperature in a reaction of reducing tin with hydrogen.

DETAILED DESCRIPTION OF THE EMBODIMENT

Hereinafter, methods of recovering tin and nickel compounds according to the specific embodiments of the present invention will be explained in further detail.

According to an embodiment of the present invention, a method of recovering tin and nickel compounds is provided, which includes: the steps of subjecting scrap steel balls for barrel plating to a heat treatment at a temperature of 300° C. to 700° C.; grinding and sorting the heat-treated scrap; adding a tin compound and a nickel compound that are separated from the grinding and sorting step to an acidic solution; filtering the acidic solution having the tin and nickel compounds added thereto; subjecting residues from the filtering step to a hydrogen reduction treatment at a temperature of 600° C. to 1000° C. to recover tin; and subjecting the recovered tin to electrolytic refining.

The present inventors researched the method of recovering tin and nickel from the scrap steel balls for barrel plating (e.g., the dummy balls obtained as byproducts from a barrel plating process for the electronic parts) and experimentally reached the present invention consisting of applying eco-friendly dry pretreatment and subsequent processes including hydrogen reduction and electrolytic refining under certain conditions to make it possible to easily separate an excess amount of an iron component from tin and nickel compounds having a powder form, while reducing the amounts of chemicals to be used and waste, shortening the time for a dissolution reaction to enhance the process efficiency, and recovering tin and nickel compounds with high purity at high yields.

Specifically, in accordance with the recovery method of the tin and nickel compounds, the iron component may be recovered and recycled with high efficiency by conducting pretreatment using a physical means, and the nickel compound may be recovered and recycled from the solution to which only nickel is selectively leached. Moreover, the residues not being dissolved in the leaching solution are subjected to purification to allow the recovery of highly pure tin. In particular, the residues not being dissolved in the leaching solution are purified through certain processes of hydrogen reduction and electrolytic refining to be recovered as highly pure tin having a purity of, for example, at least 99.5%.

The scrap steel balls for barrel plating may include a material having an iron compound core (i.e., a steel sphere), the surface of which is plated with a tin compound and a nickel compound one after another or as an alloy thereof. More specifically, the scrap steel balls for barrel plating may be the dummy balls obtained as byproducts from a barrel plating process of electronic parts. The actual appearance of the dummy balls and their schematic structures are shown in FIG. 1.

In the scrap steel balls for barrel plating, the steel balls may have a different size depending on the types and the sizes of the electronic part, i.e., the subject of barrel plating. For example, the scrap steel balls for barrel plating may have a spherical or circular shape with a longest diameter of 0.1 mm to 5 mm. The surface of the scrap steel balls for barrel plating may be sequentially plated with the tin and nickel compounds or as an alloy to form a shell layer on the core of the iron component. The thickness of such a shell layer may range from, for example, 0.5 μm to 100 μm.

Specific compositions of the scarp of the steel balls for barrel plating may vary with the characteristics of barrel plating. By way of an example, the iron based scrap may include 10 to 98 wt % of an iron component, 1 to 80 wt % of a tin component, and 1 to 80 wt % of a nickel component.

In the step of subjecting the scrap steel balls for barrel plating to heat-treatment, the difference in the coefficient of thermal expansion for each metal may bring about the separation of iron from tin and nickel. Among the components included in the scrap steel balls for barrel plating, the coefficients of thermal expansion of iron, tin, and nickel are 12.3*10⁻⁶/°C., 21.2*10⁻⁶/° C., and 13.3*10⁻⁶/° C., respectively. Accordingly, after the heat treatment, the steel balls including the iron component may be easily separated from the tin and nickel plating layers due to the difference in the coefficient of thermal expansion therebetween.

The temperature of the heat treatment for the scrap steel balls for barrel plating is not particularly limited. However, if the heat treatment is conducted at a temperature of 300 to 700° C., preferably 500 to 600° C., mass production may be readily realized and the recovery rate may also increase. In the heat treatment, too high a temperature is not preferred because it may cause the aggregation of ball particles.

The time of the heat treatment may depend on the composition and the amount of the scrap steel balls for barrel plating. By way of an example, it may take around 1 to 40 hours, but the present invention is not limited thereto.

After the heat treatment, the scarp steel balls for barrel plating are subjected to grinding and sorting and can thereby be separated into core parts mainly including the iron component and powders mainly including the tin and nickel components. The grinding of the heat-treated scrap may be accomplished by utilizing a ball mill or a vibration mill. The use of the vibration mill enables a relatively higher recovery rate. The specific structures of the ball mill or the vibration mill and the grinding times may be properly controlled depending on the composition and the amount of the scrap steel balls for barrel plating as used. The grinding may be conducted for 1 to 10 hours using any ball mill or vibration mill typically known in the art, but the details for the grinding step are not limited thereto.

In the step of sorting, one may use any apparatus and method known to be commonly used for sorting metal scrap and powders without particular limitations. For example, one may use a method of sorting with a 10-200 mesh sieve, a method of using high pressure air or wind power, or a centrifuge method, to name a few.

The core parts or the steel balls mainly including the iron component as obtained through the grinding and sorting step may be recycled directly as raw materials for steel manufacture. The powders mainly including the tin and the nickel components may be subjected to a wet process utilizing an acidic solution to recover the tin and nickel compounds.

When the powders of the tin and nickel compounds separated from the steps of grinding and sorting are added to the acidic solution, the nickel compound is leached into the solution, while tin is not dissolved and remains as a residue of the tin compound.

As the acidic solution, one may use any organic or inorganic acids known to be used for leaching a metal and a metal compound without particular limitations, and the concentration of the acidic solution is not particularly limited as well. However, for a more efficient leaching and recovery process, the acidic solution may have a concentration of 0.1 to 10 M, preferably 1 to 7 M.

In addition, the acidic solution may include a strong acid such as sulfuric acid, nitric acid, or hydrochloric acid, and preferably includes nitric acid or a mixed solution of nitric acid and hydrochloric acid.

In particular, nitric acid shows an extremely low level of leaching (e.g., a leaching rate of 1% or less) for tin so that the acidic solution preferably uses nitric acid at a concentration of 1 to 7 M. Further, nitric acid and hydrochloric acid may be mixed and used in order to increase the content of tin not being leached into the acidic solution and to decrease the contents of iron and nickel included in the residue. Specifically, it is preferred that 1 to 7 M of nitric acid and 1 to 7 M of hydrochloric acid are mixed and used at a volume ratio of 20:1 to 50:1.

The recovery of the tin and nickel compounds may include filtering the acidic solution to which the tin and nickel compounds as separated have been added. As described above, since the nickel compound is leached into the acidic solution while the tin compound is not dissolved and remains as residues therein, the filtrate being obtained from the filtering step mainly includes the nickel compound while the residue therefrom predominantly includes the tin compound.

The filtrate may include not only nickel but also iron, and the latter may be eliminated by using a precipitation method, a solvent-extraction method, an ion exchange method, or the like. Preferably, one may use a precipitation method using an alkaline compound.

Accordingly, when the pH of the filtrate obtained from the filtering step is controlled to between 2 and 5, preferably between 2.5 and 4, most of the iron component contained in the filtrate can be removed. In such a step of controlling pH, it is possible to use an alkaline compound such as sodium hydroxide, ammonia, or the like. The iron component may exist in two types of ions, i.e., Fe(II) and Fe(III). In this regard, Fe(III) may be precipitated as Fe(OH)₃ in the pH range of 2 to 5, while Fe(II) may be precipitated in the above pH range only after it is oxidized to Fe(III).

The recovery method of the tin and nickel compounds may further include a step of recovering the nickel compound by evaporating and concentrating the filtrate from which the iron component has already been removed, as described above. When the filtrate obtained after the removal of the iron component is concentrated, the nickel compound may be obtained with high purity. The methods and the apparatus that can be utilized in the evaporation and concentration of the filtrate are not particularly limited, and by way of an example, the evaporation and concentration may be conducted by heating the filtrate directly or indirectly to a certain temperature to remove water.

On the other hand, in the residue from the filtering step, the tin component may predominantly exist in the form of an oxide, and thus reducing the residue enables the recovery of tin with high purity. In particular, the reduction method using hydrogen is preferred to the reduction by carbon in order to minimize influences of carbon dioxide emission and some energy issues in the reduction process of the residues from the filtrate.

Specifically, according to an embodiment of the present invention, the method of recovering tin and nickel compounds may include a step of recovering tin by subjecting the residues obtained from the filtering step to a hydrogen reduction treatment at a temperature of 600° C. to 1000° C.

With regard to the reduction reaction of tin by hydrogen, the reaction scheme of reducing tin oxides by hydrogen may be represented by Formula (I), and the change in the free energy may be calculated by using thermodynamic data as follows. In addition, in order to trigger the hydrogen reaction, ΔG°(1)+2ΔG°(2) is calculated as set forth in Formula (4).

SnO₂+2H₂(g)→Sn+2H₂O(g) or

SnO+H₂(g)→Sn+H₂O(g)  (1)

SnO₂=Sn+O₂  (2)

ΔG ⁰(1)=586,800−215.62T(J/mol)H₂+½O₂=H₂O  (3)

ΔG ⁰(2)=−239,651+8.14T ln T−9.25T(J/mol)

ΔG ⁰=107,498+16.28T ln T−234.12T(J/mol)  (4)

The relation between the temperature and the standard free energy in the reduction reaction for tin by hydrogen is shown in FIG. 5. Such thermodynamic data show that the reduction reaction is likely to occur at a temperature of about 607° C. since the change in the standard free energy at that temperature is a negative value. As shown in the following experimental examples, when the residues from the filtering step are subjected to a hydrogen reduction treatment at a temperature of 600° C. or higher, the reduction rate may be at least 99%.

An electrolytic refining process may be additionally carried out in order to increase the purity of tin as recovered from the hydrogen reduction treatment. The electrolytic refining process may be conducted under proper conditions depending on the amount of tin, the rectifier or the electrolytic bath as used, or the like. In order to enhance the efficiency of removing impurities contained in the tin as recovered from the aforementioned step and to recover the same with higher purity, however, the electrolytic refining process may be carried out at a temperature of 10° C. to 60° C., preferably 20° C. to 50° C. with the current density ranging from 0.04 A/dm² to 4.0 A/dm², preferably from 0.2 A/dm² to 1.0 A/dm², and the distance between the electrodes ranging from 1 mm to 500 mm, preferably from 10 mm to 200 mm, and more preferably from 70 mm to 120 mm.

In addition, the voltage that can be used in the electrolytic refining process may be properly controlled depending on the amount of tin used, the rectifier or the electrolytic bath as utilized, or the like, and by way of an example, it can be controlled to 15 volts or lower, and preferably in the range between 0.1 volts and 5.0 volts.

In accordance with the foregoing embodiments of the present invention, a method of recovering tin and nickel compounds with high purity with high efficiency from the scrap steel balls for barrel plating through simple steps without using an excess amount of solvent is provided.

Hereinafter, the present invention will be described referring to the following examples. However, these examples are merely illustrative of the present invention, the scope of which shall not be limited thereby.

Example 1 Separation and Recovery of Nickel and Tin Compounds from Dummy Balls Obtained from Barrel Plating for Electronic Parts

1. Raw Materials and Heat Treatment

10 kg of scrap of steel balls obtained from barrel plating for electronic parts (i.e., dummy balls with an average diameter being about 550 μm and a thickness of the plating layer of tin/nickel being about 10 μm) was placed in an SUS container and heated. The results of analyzing the dummy balls with an inductively coupled plasma (ICP, GBC Integra XL) showed that they included 85.3 wt % of iron (Fe), 8.7 wt % of tin (Sn), and 5.9 wt % of nickel (Ni). A SEM image of the dummy balls being used is shown in FIG. 2.

2. Grinding and Sorting

(1) The dummy balls as heat-treated were ground using a ball mill or a vibration mill. In case of using the ball mill, the grinding was conducted by mixing 1 kg of raw materials with 2 kg of three types of steel balls of 2 mm, 5 mm, and 10 mm. After the completion of the grinding, an 80 mesh sieve was used to separate the steel balls of the iron component from the powders of the tin and nickel components.

(2) The recovery ratios of iron (Fe) depending on specific heating conditions, and the methods of grinding are compiled in Table 1 and Table 2 below. In this regard, the recovery ratio of iron was calculated from the ratio of the weight of iron as separated to the weight of iron being included in the raw materials.

TABLE 1 Iron recovery rate depending on heating conditions and grinding methods (heating time: 3 hours) Heating Ball mill Ball mill Vibration mill temperature grinding grinding grinding (° C.) (3 hours) (3 hours) (1 hour) 300 83.7% 89.3% 94.7% 400 86.5% 90.9% 95.3% 500 88.8% 93.0% 97.8% 600 88.2% 92.5% 98.7% 700 88.1% 95.6% 99.3%

TABLE 2 Iron recovery rate depending on a heating temperature (treated with the ball mill grinding for 6 hours) Heating Heating Heating time temperature 500° C. temperature 600° C. 1 88.0% 88.6% 3 93.0% 92.5% 7 92.0% 92.3% 11 94.2% 95.1% 23 93.3% 96.0%

As shown in Table 1 and Table 2 above, it was confirmed that when the iron scrap was heat-treated and then ground and sorted, at least 80% of iron could be recovered. As shown in Table 1, some increase in the grinding time led to a higher recovery rate of iron, and the vibration mill grinding resulted in a higher rate of the iron recovery than the ball mill grinding. In addition, as shown in Table 2 above, between 300° C. and 700° C., the higher the temperature of the heat treatment was, the higher the iron recovery rate was accomplished.

(3) Results of XRD Analysis

The samples being heat-treated at 600° C. for 3 hours were subjected to ball mill grinding for 6 hours, and XRD analysis was performed on the powders being sorted. As shown in the results of the XRD analysis of FIG. 3, it was confirmed that the powders of the tin and nickel components were an alloy of Ni₃Sn₂ and a tin oxide of SnO₂, respectively.

3. Addition of the Powders of the Tin and Nickel Components as Separated with an Acidic Solution

(1) The samples being heat-treated at 600° C. for 3 hours were subjected to ball mill grinding for 6 hours and sorting to prepare the powders of the tin and nickel components, which were then subjected to a reaction at a temperature of 80° C. in a nitric acid solution having a concentration of 1 M, 3 M, 5 M, or 7 M for 10 minutes, 20 minutes, 30 minutes, 40 minutes, 60 minutes, and 90 minutes, respectively. The amount of the compound being leached from each solution was measured and the results are shown in FIG. 4.

As shown in FIG. 4, the highest leaching efficiency was obtained when the reaction occurred in a 3 M nitric solution for 20 to 40 minutes, and after the 30 minute reaction, the tin content in the residues reached around 88 wt %.

(2) A 5 M hydrochloric acid solution was added to 1 L of a 3 M nitric acid solution, and to such a mixed acid solution, the powders of the tin and the nickel components as obtained above (i.e., heat-treated at 600° C. for 3 hours, subjected to ball mill grinding for 6 hours, and sorted) were added and reacted at 80° C. for 30 minutes.

When 10 mL of a 5 M hydrochloric acid solution was added to 1 L of a 3 M nitric acid solution, the leaching rate of the tin compound was below about 5 wt % and the tin content in the residues that had not been leached was in the order of about 98 wt %.

4. Separation and Recovery of the Nickel Compound and the Tin Compound

The solution as obtained from the 30-minute reaction in the 3 M nitric solution of the above section 3-(1) was filtered with a filtering device using a Whatman filtering paper 3 (Qualitative Circles 150 mmΦ). In the filtrate as obtained, the content of nickel was 95 wt % and the content of iron was 5 wt %.

By adding ammonia or sodium hydroxide to the filtrate and adjusting its pH to 4, iron in the filtrate was removed by using an iron hydroxide precipitation method. The solution was analyzed with an ICP device to confirm that it contained a pure form of nickel. Then, the solution was evaporated and concentrated to give a nickel compound.

Examples 2 and 3 and Comparative Example 1 Reduction Treatment for Tin as Recovered

The residues from the filtering step as obtained in Example 1 were subjected to a reduction treatment as follows.

(1) The experimental device being used was a furnace manufactured by Koryo Electric Furnace Development Co., Ltd., largely consisting of a heating part, a temperature controlling part, and a gas controlling part. A SiC heating element was used in the heating part, and an SUS 316 chamber was used for temperature control in the reduction reaction. The size of the chamber was 200 mm×200 mm×400 mm (width×length×height). The temperature controlling part adopted an R-type pyrometer and a PID temperature controlling device. The gas controlling part was designed to allow three types of gases to flow, and was equipped with a flow meter to regulate 5 L/min so as to allow determined amounts of hydrogen gas and nitrogen gas to flow in the furnace for the experimentation.

(2) With using a ceramic crucible, about 10 g of the residues obtained from the filtering step was taken as a sample to carry out reduction experiments. Specifically, a nitrogen gas flowed at a rate of 1 L/min for 10 minutes and with hydrogen being injected at a flow rate of 1 L/min, the hydrogen reduction treatment was conducted for 60 minutes at a temperature of 500° C. (Comparative Example 1), 700° C. (Example 2), and 900° C. (Example 3), respectively.

(3) After the completion of the hydrogen reduction treatment, the flow of the hydrogen gas was stopped and the nitrogen gas flowed until the temperature of the chamber dropped to about 200° C. so as to prevent oxidation of the chamber. In addition, cooling water was allowed to flow into the chamber during the experiment for the purpose of avoiding an increase in the temperature of the SUS chamber. The heating rate was 5° C./min and the cooling type was natural cooling.

The results of the hydrogen reduction treatment are shown in Table 3 below.

TABLE 3 Initial sample Sample Reduction amount amount after rate Reduction conditions (g) the reduction (g) (%) Comparative Example 1 10.00 8.67 90.8 (500° C., 60 min) Example 2 10.00 7.83 100 (700° C., 60 min) Example 3 10.00 7.81 100 (900° C., 60 min)

As shown in Table 3, in Comparative Example 1 adopting a reduction temperature of 500° C., the reduction rate was about 91%, indicating that not all residues of the sample were turned into tin. In contrast, in Examples 2 and 3 adopting reduction temperatures of 700° C. and 900° C., respectively, the reduction rate was 100%, indicating that the whole sample was turn into tin.

Example 4 Electrolytic Refining of Tin

The tin as obtained from Example 3 was subjected to electrolysis as follows.

(1) The rectifier used in the electrolysis was a high frequency insulated gate bipolar transistor (IGBT), which was manufactured by KooSoo Heavy Electric Co. Ltd. and designed to have capacity conditions of a voltage of up to 15 volts and a current of up to 50 A. The electrolysis bath being used was a product of Kunyoung International Co. Ltd., with a capacity of about 37 L and a size of 220×260×650 mm (width×length×height).

With using a Teflon heater, the temperature was controlled up to 80° C., and a magnet pump was utilized in order for the electrolyte to be circulated consistently. The electricity flowed through a copper busbar (diameter: 11Φ, length: 300 mm), and the length between the electrodes was designed to be adjustable. The electrolyte used in the electrolysis was H₂SiF₆+H₂SO₄, and the composition of the electrolyte was 60% sulfuric acid (H₂SO₄) and 40% hydrosilicofluoric acid (H₂SiF₆) as calculated by weight ratio. In this regard, the concentrations of sulfuric acid and hydrosilicofluoric acid were set to be 6% and 5%, respectively.

The electrolyte was made to circulate consistently and was supplied to the electrolysis bath through a filter in order for the residue of the electrolyte to be eliminated. The used amount of the electrolyte was about 40 L in the electrolysis bath and 10 L in the assistant electrolysis bath for circulation of the electrolyte.

(2) Specifically, for the electrolytic refining experiment, the tin obtained from the reduction treatment in Example 3 (purity: around 99%) was provided as an anode and tin with a purity of about 99.9% was provided as a cathode. The temperature and the pH of the electrolyte being used were about 25° C. and about 1.4, respectively, and the electro-conductivity was about 20.2 S/m.

To determine the influence of electrolytic refining depending on the distance between the electrodes, the electrolysis was carried out with the distance between the electrodes being 50 mm (Example 4), 75 mm (Example 5), and 100 mm (Example 6), respectively. In this regard, the value of the current density was 0.4 A/dm², the voltage was changed between 0.69 and 1.14 V, the temperature of the electrolyte was 25° C., and the time for electrolysis was about 3 hours.

In addition, except that the distance between the electrodes was 100 mm, the temperature of the electrolyte was controlled to be 25° C., and the current density was 0.8 A/dm², electrolysis was conducted in the same manner as in Examples 4 to 6 (Example 7).

Electrolysis was also conducted in the same manner as in Examples 4 to 6, except that the temperature of the electrolyte was controlled to be 40° C. (Example 8) and 50° C. (Example 9) with the distance between the electrodes being 100 mm, and the current density being 0.4 A/dm².

(3) The efficiency of the electric current in the electrolysis conducted in Examples 4 to 9 was determined in the following manner.

The tin metal electrodeposited onto the cathode was attached in a sponge form and could be easily separated from the cathode. After the tin metal sponge was separated was dried at 100° C. for 24 hours, its weight was measured to calculate the efficiency of the electric current in accordance with Mathematical Formula I below, and regarding the efficiency of electric current for the electro-deposition, it was assumed that the oxidation value of an Sn ion participating in the reaction was 2.

$\begin{matrix} {{{Efficiency}\mspace{14mu} {of}\mspace{14mu} {Electric}\mspace{14mu} {Current}\mspace{14mu} (\%)} = \frac{\begin{bmatrix} {\begin{pmatrix} {{Electro}\text{-}{deposited}} \\ {{amount}\mspace{14mu} {on}\mspace{14mu} {the}\mspace{14mu} {cathode}} \end{pmatrix}*} \\ {96\text{,}500*2*100} \end{bmatrix}}{\begin{bmatrix} \begin{matrix} {\left( {{Atomic}\mspace{14mu} {weight}\mspace{14mu} {of}\mspace{14mu} {Sn}} \right)*} \\ {\left( {{Electric}\mspace{14mu} {current}\mspace{14mu} {as}\mspace{14mu} {applied}} \right)*} \end{matrix} \\ \left( {{time}\mspace{14mu} {as}\mspace{14mu} {applied}} \right) \end{bmatrix}}} & \left\lbrack {{Mathematical}\mspace{14mu} {Formula}\mspace{14mu} 1} \right\rbrack \end{matrix}$

The results of the efficiency of electric current as calculated are shown in Table 4.

TABLE 4 Exam- Exam- Exam- Exam- Example 4 Example 5 ple 6 ple 7 ple 8 ple 9 Efficiency 75% 89% 92% 82% 94% 94% of electric current

As shown in Table 4, as the distance between the electrodes increases to 50 mm, 75 mm, and 100 mm, the efficiency of electric current was found to increase up to about 75%, 89%, and 92%, respectively. In Example 7 (the distance between the electrodes: 100 mm, the temperature of the electrolyte: 25° C., the current density: 0.8 A/dm²), the efficiency of electric current decreased by about 10% in comparison with Example 6 applying 0.5 times current density. In case of Example 8 and Example 9 with the temperature of the electrolyte being 40° C. and 50° C., respectively, the efficiency of electric current was confirmed to relatively increase up to about 94%.

(4) Determination of the Purity of the Tin Metal as Recovered

Regarding the content of the impurity contained in the tin metal as recovered, the detectable elements in the cathode being used were analyzed to measure their contents by using inductively coupled plasma (ICP, GBC Integra XL). The purity of the tin as recovered was calculated from the content of the tin obtained by excluding the amount of the impurity contained therein. The results of such experiments are shown in Table 5 below.

As shown in Table 5 below, the results of the efficiency of removing impurities in the examples show that in case of Co, Ni, and Fe, at least 90% thereof was eliminated. In particular, for Ni and Fe that could have been incorporated from the raw materials being used, around 98% thereof was removed. In case of Al, Na, Ca, Si, and Cu, around 50% thereof was found to be eliminated, but the amount of Pb increased in comparison with the amount included in the anode.

The purity of Sn being recovered in Examples 4 to 9 was at least 99.5% in all cases, and in particular, when the distance between the electrodes was 100 mm, the current density was 0.4 A/dm², and the temperature of the electrolyte was set to be 40° C. and 50° C., it was possible to achieve purity of about 99.9%.

TABLE 5 Purity of Sn Classification Al Na Ca Co Pb P Ag Si Ni Fe Cu (%) Anode 179 254 509 152 10 325 189 1250 1442 2935 3181 98.96 Example 4 62 133 120 12 921 263 36 487 14 46 781 99.71 Example 5 60 125 140 11 891 466 20 324 5 36 669 99.73 Example 6 59 119 117 8 816 168 10 328 9 28 335 99.80 Example 7 55 121 93 1 793 110 5 357 3 19 178 99.83 Example 8 51 93 87 20 102 1 1 154 6 35 402 99.90 Example 9 30 60 68 21 84 1 1 206 3 20 324 99.92 * In Table 5, the unit of the content for each component is ppm. 

What is claimed is:
 1. A method of recovering tin and nickel compounds, which comprises the steps of: subjecting scrap steel balls for barrel plating to a heat treatment at a temperature of 300° C. to 700° C.; grinding and sorting the heat-treated scrap; adding tin and nickel compounds being separated from the grinding and sorting step to an acidic solution; filtering the acidic solution having the tin and nickel compounds added thereto; subjecting residues of the filtering step to a hydrogen reduction treatment at a temperature of 600° C. to 1000° C. to recover tin; and subjecting the recovered tin to electrolytic refining.
 2. The method of recovering tin and nickel compounds in accordance with claim 1, wherein the scrap steel balls for barrel plating comprise 10 to 98 wt % of an iron component, 1 to 80 wt % of a tin compound, and 1 to 80 wt % of a nickel compound.
 3. The method of recovering tin and nickel compounds in accordance with claim 1, wherein the scrap steel balls for barrel plating have a spherical or circular shape having a longest diameter of 0.1 to 5 mm.
 4. The method of recovering tin and nickel compounds in accordance with claim 1, wherein the scrap steel balls for barrel plating are obtained from a barrel plating process for an electronic part.
 5. The method of recovering tin and nickel compounds in accordance with claim 1, wherein grinding the heat-treated scrap steel balls for barrel plating is carried out by using a ball mill or a vibration mill.
 6. The method of recovering tin and nickel compounds in accordance with claim 1, wherein the acidic solution with the tin and the nickel compounds as separated in the grinding and sorting step added thereto has a concentration of 0.1 to 10 M.
 7. The method of recovering tin and nickel compounds in accordance with claim 1, wherein the acidic solution comprises nitric acid, or a mixture of nitric acid and hydrochloric acid.
 8. The method of recovering tin and nickel compounds in accordance with claim 1, further comprising a step of controlling pH of the filtrate of the acidic solution having the tin and nickel compounds added thereto to between 2 and 5 to eliminate the iron component.
 9. The method of recovering tin and nickel compounds in accordance with claim 8, further comprising a step of evaporating and concentrating the filtrate obtained after the iron component is eliminated to recover the nickel compound.
 10. The method of recovering tin and nickel compounds in accordance with claim 1, wherein the electrolytic refining is carried out at a temperature of 10° C. to 60° C. with a current density of 0.04 A/dm² to 4.0 A/dm² and a distance between electrodes of from 1 mm to 500 mm. 